The document you are following is written for OpenBSD 3.7. We are essentially one month from the code lock for OpenBSD 4.7 release. You do understand that you are using 5 years old document?

I know people running irssi chroot-ed. I have never heard of anybody using
systrace to control irssi. You now realize why OpenBSD developers are so opposed to mandatory access control (MAC) It simply doesn't work because proper policies are so hard to write.

I would be curious myself to see if you get a different answer from somebody else. Above being said about MAC and in particular systrace I want to add that Systrace is very useful to people who are porting software to OpenBSD but that is another story.